1. Field of the Invention
The present invention generally relates to a medium conveying apparatus, an image forming apparatus, and a medium conveying system.
2. Description of the Related Art
An image forming apparatus such as a copy machine or a printer has multiple detection sensors (e.g., reflection type optical sensors) provided in its paper conveying path for detecting a paper conveying status (e.g., paper conveying position, paper jam). By making slight adjustments of paper conveying speed according to the output of the detection sensors, the position of the image to be formed on the paper can be accurately matched with a desired position. Thereby, degradation of image quality due to, for example, position deviation can be prevented. In a case where conveying failure (e.g., paper jam) occurs, the location of the conveying failure can be detected according to the output of the detection sensors.
Therefore, the detection sensor that is provided in the paper conveying path plays a significant role in the image forming apparatus. However, providing multiple detection sensors in the paper conveying path increases cost and complicates the structure of the image forming apparatus. This limits the layout inside the image forming apparatus.
In view of the limited layout, there is a known method of detecting a paper jam by detecting the torque of a roller that holds and conveys paper and comparing the value of the detected torque with a predetermined value (see, for example, Japanese Laid-Open Patent Publication No. 9-236958). With this method, paper conveying failure can be detected with a simple configuration requiring no detection sensors.
However, although a paper jam of a conveying unit can be detected with this known method, the paper conveying status cannot be detected in a case where paper is regularly conveyed by the conveying unit. That is, in order to detect paper conveying status other than such a paper jam, a detection sensor or the like is to be provided in the image forming apparatus.